Work vehicles known as pickups or light trucks are designed to behave according to existing security guidelines or regulations in the event of frontal or side impacts or collisions. However, regarding rollovers, there are no standard guidelines to evaluate the vehicle behavior, nor any minimum parameters for said vehicles to achieve.
In recent vehicle models, it is noticeable that manufactures have increased the strength of pickup cabins, in order to prevent buckling or collapse of the cabin during rollovers.
In this sense, in order to test the strength of the structure, the Insurance Institute for Highway Safety (IIHS) carries out a test in which the vehicle is placed under a press and subjected to pressure from a pressing plate above the intersection between the A pillar and the roof, as well as the surrounding area, the pressure being capable of producing a 5-inch deformation of the cabin.
In order to compare test results obtained with different vehicles, the IIHS has developed a coefficient which is obtained by dividing the load required to obtain a 5-inch deformation by the weight of the vehicle. Therefore, if a pickup weighting 2000 kg required 8000 kg of force in order to reach a 5-inch deformation, the coefficient for this vehicle is 8000kg/2000kg=4.
Usually, coefficients are in the range from 3 to 4. A value of 4 is needed to reach a “Good” rating, according to IIHS test, while a coefficient of 4.75 is the highest coefficient obtained in pickup cabin tests.
In other words, for a 2000 kg pickup, a typical weight for various pickup models, the load needed to produce a 5-inch deformation varies from 6 to 8 tons up to 9.5 tons for the highest coefficient of 4.75.
Even so, in some activities with a high rollover occurrence due to the type of roads and terrains involved and lack of proper driver training, such as mining and oil well activities, in which severe cabin crushing or buckling can occur, it is a common practice to reinforce the cabin of pickups with the purpose of reducing the risk of injury to the occupants in the event of a rollover.
Different kinds of rollover protection devices for pickups are known, which can be classified as internal and external protections.
Internal Protection Devices:
Internal protections, also known as “Cages” or “Roll Cages, are frames or structures installed within the cabin, constructed from beams or tubes and usually assembled inside the passenger space with bolts or other fastening means.
These types of protection devices have several drawbacks, such as, for example:
1) The protection structure itself presents a hazard to the occupants of the vehicle in the event of a collision or other accidents, because the cage comprises solid elements located within the passenger area, which will often hurt the occupants;
2) These protection devices interfere with the vehicle compartments in the event of frontal or side collisions, as it alters the load/deformation conditions of the original vehicle. This can result in an undesirable deceleration increase of the vehicle occupants;
3) They limit the habitability, that is to say the space and comfort of the cabin;
4) The protection installation is cumbersome, especially on recent pickup models as it comprises more voluminous dashboards and upholstery.
There are some known variations of said protections, which involve designing the cage or safety structure to be located underneath the original upholstery, with minor modifications.
However, this type of solutions requires:
a) A high construction cost due to the precision required in shaping the tubes, machined assemblies, etc.;
b) A significant degree of disassembly of the dashboard and upholstery;
c) Long installation time per unit;
d) High cost, incompatible for uses not requiring such a level of aesthetic and functional details.
In conclusion, this alternative only solves one aspect of the disadvantages of internal cages; since the cage is underneath the upholstery no longer presents a danger to the occupants, yet the other disadvantages still remain.
Moreover, in order for the internal protection system to be effective, it should deform at the same time and in similar dimensions as the deformations occurring on the vehicle cabin, which may be termed as “joint deformation”. This joint deformation combines the resistance to deformation provided by the reinforcement system with the strength of the original cabin, both deforming simultaneously. During joint deformation, the protection system needs only to provide enough resistance to the cabin to allow an acceptable deformation amplitude, such as 5 inches according to IIHS. Achieving this joint deformation is highly important, as this deformation reduces the deceleration affecting the driver and passengers during a rollover event.
Precisely, in order to mitigate the deceleration, said test protocols establish maximum tolerated deformation amplitudes, always giving priority attention to the reduction of the internal physical space that must be inhabited by the occupants.
Cages and safety structures allow, among their characteristics, to comply with the condition of “joint deformation” together with the cabin. This behavior is the result of proper design complemented by virtual and practical tests directed at the evaluation and adjustment of this feature.
External Protection Devices
There are two types of external protection devices:
U.S. Pat. No. 3,622,177 by Notestine, granted on Nov., 1971, and U.S. Pat. No. 4,900,058 by Hobrecht, granted on February, 1990, describe protection designs as accessory equipment for units exposed to rollover conditions, such as four-wheel drive vehicles, vans, sports, etc. Furthermore, U.S. Pat. No. 7,338,112 by Gilliland, granted on March, 2008, describes a tube structure placed outside the vehicle.
These types of structures, in addition to not being aesthetically pleasing, expand and extend the vehicle profile. They add dimensions and protrusions that are unsuitable for transit in places where they might get stuck, also affecting the aerodynamic features of the vehicle and consequently increasing fuel consumption and noise generation, which causes discomfort to the occupants of the vehicle during long trips.
As a result of these characteristics, these structures located on the exterior of the vehicle are usually excluded from call for tenders for vehicle equipment carried out by users of a large number of pickups.
Another exterior cabin protection device of said type is known in the art as “Black Swan”, developed by Delta-V Experts SA, which consists of a structure that is fixed to the truck bed and projects as a cantilever beam over the cabin roof. Said solution is reasonable for application in single cabin vehicles, since the extent of the cantilever is approximately the same as the length of the cabin.
However, since this protection utilizes a cantilever beam, its front end is exposed to a moment of twice the magnitude, i.e. force*length vs. force*length/2, in relation with other protection devices where all ends are supported, e.g. by being applied transversely from side to side of the roof. Therefore, in order to obtain a similar protection with this alternative, a significant increase in materials is required, and in addition to the inherent cost, the truck is subjected to a permanent extra weight.
Given the above, the use of this option on double cabin pickups would lead to a cantilever which is twice as long as the ones needed for single cabin pickups, and the resulting moment at the front end would be four times that of protection devices that are supported from side to side on the cabin, i.e. 2×force×length vs. force×length/2. Therefore, such protection device would require the structure to withstand four times more stress in order to provide the cabin with the same protection as transversally fixed reinforcements. The greater added weight to the vehicle due to the structure and the space occupied on the bed by this type of designs discourage their use on double cabin vehicles.
In order to reduce the length of the cantilever, some variations adopt a higher position on the front end. With this increased height, the structure protects the cabin due to a line formed between the front end of the cantilever and the nose of the vehicle, sheltering the vulnerable areas of the roof without the need for a longer cantilever.
However, such a large projection is susceptible to getting stuck on the terrain when moving lengthwise, before or during the rollover event. In these cases the deceleration is significant and compromises the survival of the occupants.
Another external protection system is the HALO SYSTEM, developed by Safety Engineering International (SEI).
U.S. Pat. No. 7,717,492 by Safety Engineering International (SEI), granted in May, 2010, describes a device intended to improve the behavior of vehicles during a rollover event. Said device is based on the mechanics of rollover in which the truck is expected to roll around its center mass axis, said axis being transversally oriented to the direction of the successive rolls (barrel rolls).
According to this concept, it is considered that when rolling over with the roof upon the ground there is a radius between the center mass axis of the vehicle and the ground. However when the vehicle continues rolling, it will touch the ground with one of the corners of the roof, and since said radius at that point is greater, the truck will experience an upward vertical acceleration, or in cases where the structure formed by the pillar and the roof buckles, the roof will collapse.
In order to eliminate said vertical acceleration, the HALO system proposes placing exterior arcs over the roof in order to allow the vehicle to roll without experiencing said supposed vertical accelerations, as shown in FIG. 1 herein.
However, the HALO system does not take into account that, due to rollover mechanics, when the wheels come into contact with the ground they will also produce an upward vertical acceleration of the vehicle, i.e. bouncing. The vehicle will rise and then fall, impact on the ground and continue rolling. It's during this impact that the roof and consequently, the pillars supporting it, suffer the greatest deformation stress, and the HALO system is not properly designed to absorb this stress in an appropriate manner.